It was open house at the Met, when the hoary and staid home of grand opera allowed the unwashed rabble (actually, many seemed to be opera lovers) through its doors, free, to wander the house, view exhibits and listen to a question-and-answer session.

The highlight was a dress rehearsal of Puccini’s “Madama Butterfly,” which will open the season Monday in a gala evening. The house was full and enthusiastic, listening attentively and cheering forcefully.

“This is incredible,” said Jill Goldberg, a chiropractor who has homes in New York and Milford, Mass. “This is what makes New York like nowhere else in the world.”

Actually, open houses at performance halls are not completely new. But it is the first time the Met has done such a thing. The event was part of a carefully calibrated buildup of publicity set in motion by Peter Gelb, the new general manager, in the days leading up to Monday’s opening night.

It included announcements that the Met will simulcast in movie theaters, broadcast opening night in Times Square and put performances on a dedicated Sirius satellite radio channel. The Met also opened a lobby art gallery and draped a banner in front of the house with the opera’s title in Japanese characters.

Mr. Gelb has said he wants to generate excitement about the art form by making it more accessible, relevant and theatrical.

During a brief intermission interview, he said, “This is opera as it should be — music and theater in perfect harmony,” referring to the visually striking production by Anthony Minghella, the film and theater director. Later, Mr. Gelb said many people had come up to him to say thank you.

“The reaction was incredibly positive,” he said. “It was a very powerful experience for people inside the house as well as outside. It’s heightened the sense of community.”

The open house was not completely open. Tickets were necessary to enter the doors, although they were free. About 3,000 were passed out by noon on Wednesday, some to people who had been waiting much of the night. Those tickets included a chit for a free lunch: three finger sandwiches with slivers of arugula, cheese and turkey, two bottles of water and two cookies.

In the comprimario role of mayor, Michael R. Bloomberg took the stage after the first intermission.

“Thanks to Peter for bringing this opportunity to everybody,” he said. “Anybody who’s said there’s no free lunch hasn’t met you. This is what’s wonderful about New York.”

Inside the auditorium, there were few neckties and even fewer suits, with a higher quotient of denim and plaid than at most Met performances. One young woman had green hair. Public relations officials from other Lincoln Center residents were on hand, perhaps to get ideas. A row of photographers with large telephoto lenses snapped away during the performance, as at a basketball game.

A number of those present said they had never been to the Met, or rarely went to the opera at all. The free tickets were a lure. Others were brought by friends and relatives.

During the first intermission, people munched their lunches along the sweeping staircases, on the balcony or standing in the lobby. They wandered into the Eleanor Belmont Room, a club used by members of the Metropolitan Opera Guild, which Eleanor Belmont founded, past a sign saying “Members Only.”

“Members only? Excuse me!” one woman said.

After the performance, Mr. Minghella, other members of the production staff, the music director James Levine and the cast sat in a row and answered a few questions from a moderator.

Then a Met official invited people to take a walk across the stage. Hundreds lined up and passed from left to right along two upside down carpets, to protect the highly polished floor, designed to reflect off the production’s overhead mirror. Stagehands answered questions. People craned their necks and took pictures.

“Oh my God, it’s unbelievable,” Mary Gomez of the Upper West Side said, adding that she was a regular ticket buyer.

Some sang out notes or phrases. One of the visitors was Marguerite Scully, a 29-year-old soprano. Speaking to no one in particular, she looked out at the house and said: “I’ll be back here. Don’t worry.”